Solid particle erosion of the components of a steam turbine occurs due to carryover of particles from the steam boiler and piping upstream of the turbine. The solid particles become entrained in the steam flow path. As they pass through the steam turbine, the particles cause damage to both the stationary and rotating parts of the turbine that degrade steam turbine performance and mechanical reliability. The solid particles may be deposited throughout the steam path or may exit the steam path into steam extractions that feed the feed water heaters of the cycle. However, since the particles are transported by the main steam flow through the steam turbine steam path, they have the opportunity to inflict considerable damage to the steam path before they are deposited or expelled from the main steam flow. This damage can include erosion of the rotating and stationary buckets and partitions respectively, erosion of the rotating tip covers or tenons, erosion of tip sealing devices such as spill strips and erosion of stationary structures over the tips of the rotating buckets.
Various apparatus and methods have been proposed and utilized to minimize the impact of the solid particles on the rotating and stationary parts of steam turbines. For example, in U.S. Pat. No. 4,776,765 a protective device is disposed over a portion of the suction side of the partition to prevent solid particle erosion of the trailing edge of the partition due to rebound of particles from the leading edge of the buckets. Other apparatus and methods for minimizing or eliminating solid particle erosion in steam turbines include solid particle erosion resistant coatings such as disclosed in U.S. Pat. Nos. 4,704,336 and 4,615,734. While many of these and other efforts to minimize or eliminate solid particle erosion have been tried in the past, solid particle erosion in steam turbines remains a continuing problem for the various parts along the steam path. Accordingly there has developed a further need for apparatus and methods to minimize solid particle erosion of steam turbine components.